RE: Receiver battery toggle?
Not that I've seen... why would you want to do this? seems to me it would just add complexity and yet another common point of failure. The biggest safety benefit to running two batteries is when you use two separate channels on the receiver, batteries and switches... this way you have independent batteries and switches powering the receiver... one set fails the other is still powering everything. If your just after longer flight times just Y two like batteries into the switch... this doubles your flight time yet offers no real redundancy for failure... unless just one battery fails.
John